Sensing devices are used in boreholes (e.g., oil wells, gas wells, observation wells, other wells, etc.) for sensing operations. Placing the sensors within a borehole has benefits over placing the sensors at or above the ground surface such as, for example, improved signal data resolution and the elimination of filtering of acoustic energy signals by the earth's weathering layer. One challenge of placing the sensors within a borehole is stabilizing the sensor within the borehole; in other words, establishing rigid mechanical coupling between the borehole and the sensor.
Attempts have been made to clamp such sensors within a borehole. One example is a remotely controlled electric motor which extends a clamp arm to lock a geophone sensor in position within the borehole. Other conventional sensors have used hydraulic motor actuators to extend and hold a clamp arm in place within a borehole. However, these conventional motorized actuators (e.g., electrical and hydraulic motor actuators) suffer from a number of deficiencies. Such deficiencies include, for example, high cost, inconsistent reliability, and technical complexity, among others. Further, such actuators require continuous power to maintain clamping force within a borehole.
Passive systems (that continuously provide clamping without actuation) such as high strength magnets and bow spring clamps have been used to secure a sensor within a borehole; however, such systems do not achieve a desired level of clamping force within the borehole, thereby resulting in suspect sensing data. Further, since these clamping systems are always engaged they create a substantial drag force (e.g., due to friction with the inside of the borehole). In order to overcome this drag force, significant weights are undesirably added to the system to pull the sensor array down through the borehole.
Thus, a need exists for, and it would be desirable to provide, improved borehole sensing and clamping systems.